My long-term career goal is to become an independent scientist with a primary focus on understanding the genetics and cellular origin of cancer and relating these to the cancer stem cell (CSC) phenotype. The research described in this proposal is designed to answer a fundamental question in cancer biology: how a CSC is formed from an originally normal cell? Specifically, I propose to use a novel mouse model of human breast cancer initiated by chromosomal translocation to study this. This model is unique in that it provides an opportunity to identify the affected population of cells early in the evolution of cancer. The specific aims of this proposal include using this translocation-initiated breast cancer model to 1. purify target cells of the cancer and characterize their earliest molecular changes after the initial oncogene expression. 2. identify, isolate and characterize cancer stem cells. 3. study contributions of genetic/epigenetic changes in several affected genes/pathways to the cancer stem cell phenotype. 4. perform cross-species comparison with human breast cancer at the molecular level. For the immediate future, I will continue my current work on this mouse model to identify and characterize target cells of this type of cancer. I will also start to identify CSCs in this model and validate the model by performing cross-species comparison with human breast cancer at the molecular level. The K99/R00 award would allow me to obtain additional training on stem cell biology, on solid tumor biology, and on bioinformatics/computational biology, under the mentorship of Dr. Stuart Orkin. The training program in hematology and oncology at Children's Hospital and Dana Farber Cancer Institute brings together the resources of both institutions as well as those from Harvard Cancer Center and provides an excellent environment for the completion of training during the mentored phase, which should facilitate a smooth transition to independence. During the independent phase, I will continue my study on CSCs in this model and compare them to the cells from which they derive and the bulk of tumor cells to which they differentiate. More importantly, I will identify and validate additional mutations/pathways that may contribute to the CSC phenotype, and assess their potential as novel therapeutic targets for human breast cancer. In summary, I propose to exploit a novel mouse model of human breast cancer as a paradigm to study CSCs and their corresponding normal target cells, for the purpose of developing rational therapeutics to eliminate cancer.